1. Field of Use
This invention relates generally to multi-stage gas compressor systems such as are used in refrigeration systems or the like and, in particular, to desuperheater means for such compressor systems.
2. Description of the Prior Art
A typical compression type refrigeration system generally comprises a evaporator, a motor-driven compressor and a condenser. A refrigerant, such as Freon or the like, which is under low pressure is evaporated in the evaporator which, for example, takes the form of a coiled pipe in a cooling or freezing compartment. This evaporation lowers the temperature in the compartment. The compressor draws away the vapor from the evaporator, compresses it, and passes it to the condenser where it parts with its heat. As a result of the combination of increased pressure and loss of heat, the refrigerant condenses from the gaseous to the liquid phrase. Finally, the liquid refrigerant is expanded to a lower pressure and is returned to the evaporator, whereupon the foregoing cycle is repeated as necessary.
In some large commercial type refrigeration systems, the pressure spread between the gaseous and liquid phase of the refrigerant is so great that a single stage compressor cannot compress the gas to the liquid phase. Therefore, it is necessary to employ a multi-stage compressor system which embodies two or more compressors connected in series with one-another or a multi-stage compressor in which two or more stages in a common housing are connected in series with each other.
In such a multi-stage compressor system, conditions arise which necessitate provisions of some means to desuperheat the partially compressed discharge gas from the first compressor or first compressor stage (both hereinafter sometimes referred to as the "first stage") before it is fed to the second compressor or second compressor stage (both hereinafter sometimes referred to as the "second stage").
First, the second stage is subject to overheating if the hot first stage discharge gas is introduced directly into the second stage suction.
Second, the second stage compressor efficiency is increased if the suction is cooled, even though the second stage mass flow is greater due to the evaporated liquid refrigerant that provided the cooling. At the lower temperature, the suction gas has a lower specific volume. Although the net efficiency effect of desuperheating the first stage discharge is positive by comparison to no desuperheating, the second stage compressor is still required to handle the additional mass flow required for desuperheating.
Prior awrt desuperheater means for multi-stage compressor systems sometimes provide for desuperheating the discharge gas of the first stage by means of a pressure vessel wherein the first stage discharge is forced through a bath of liquid refrigerant at an intermediate temperature. The heat removed by this process is not transferred to the second stage compressor. More specifically, the first stage discharge goes to the pressure vessel (desuperheater/subcooler). The discharge is directed downward below the level of liquid refrigerant maintained in the vessel. The hot discharge gas bubbling through the relatively cold saturated liquid is desuperheated. The heat given up by the discharge gas is absorbed by the liquid refrigerant and vaporizes a portion of the liquid. The desuperheater discharge gas, along with the gas created from the liquid by desuperheating is directed to the second stage. The second-stage must handle the entire flow. The aforementioned desuperheating means results in an overall increase in system thermal efficiency. As already mentioned, desuperheating is necessary. However, it does put additional load on the second stage compressor. U.S. Pat. No. 2,024,323 issued Dec. 17, 1935 to Wyld and U.S. Pat. No. 3,964,891 issued June 22, 1976 to Krieger illustrate prior art multi-stage compressor systems and cooling means therefor.